The present invention provides a bone graft harvesting drill comprised of a flexible tubular member having a hollow cylindrical drill bit mounted at its distal end. An advantage of the present harvesting drill is that it can be used to remove softer cancellous bone from between the harder cortical plates of the patient""s ilium. Specifically, the present harvesting drill can be advanced in a path between the plates of the ilium, with the drill automatically tending to deflect off the hard cortical surfaces of the bone such that the drill instead bores a path therebetween through the cancellous bone material.
In preferred aspects, the drill bit has a plurality of wavy or sinusoidal teeth which may be sharpened such that the outer surfaces of the teeth taper inwardly towards their distal ends, wherein the inner surfaces of the teeth are aligned with the walls of the drill bit. An advantage of sharpening the teeth such that their outer surfaces slant inwardly while their inner surfaces remain parallel is that as the outer surface of the distal tip of the drill bit comes into contact with the curved inner surface of the cortical plate of the patient""s ilium, the bevel or chamfer at the distal tip causes the distal tip to deflect away from the cortical bone. As the main body of the drill is flexible in radial directions, (i.e.: perpendicular to a longitudinally extending axis passing therethrough), and is preferably relatively rigid in compression along the longitudinal axis of the drill, a transverse load on the beveled end of the drill bit results in a xe2x80x9cpassive steeringxe2x80x9d condition. This xe2x80x9cpassive steeringxe2x80x9d feature of the device allows the harvesting drill to take the desired path of least resistance through the softer cancellous bone while preserving the harder cortical bone. Should the outermost edges of the drill tip instead be sharp, and not beveled or chamfered, the drill bit may instead have a tendency to catch the inner surface of the cortical bone and would undesirable pass through the ilium into the surrounding tissue. Another advantage of the beveled tip is that it is easier to push the drill through the bone during cutting.
In preferred aspects, an optional tissue removing insert is slidably received through the inner bores of the flexible tubular member and the drill bit. This tissue removing insert is specifically adapted to anchor into and, when rotated, tear away tissues which have become disposed within the inner bore of the drill bit.
In further optional aspects of the present invention, inwardly facing projections are found on the drill bit. These projections are specifically adapted to tear away tissues which have become disposed within the inner bore of the drill bit. In preferred aspects, the inwardly facing projection is formed from a C-shaped or L-shaped cut through the wall of the drill bit wherein the inner flange is bent inwardly into the bore of the drill bit. In alternate preferred aspects, a blade spans across the bore of the drill bit to tear away tissues protruding therein. An advantage of this embodiment of the invention is that the blade acts as a morcillator to pre-masticate the tissue prior to placement into the patient.
In a preferred method of using the present invention, the flexible tube and attached drill bit are rotated, however, they may instead be oscillated such that they preferentially cut through the softer cancellous tissues, avoiding harder cortical tissues.